Bone cement mixer and method

Abstract

A bone cement mixer having a cartridge housing for receiving an open bone cement cartridge filled with bone cement powder with a stirrer in the cartridge, and a cover which is fitted over the housing to define a vacuum chamber. The chamber is evacuated and monomer liquid is flowed into the bone cement powder in the cartridge in a stream that penetrates the bone cement powder and distributes monomer liquid essentially uniformly along the height of the bone cement powder. The powder and liquid are then mechanically mixed to form bone cement.

What I claim as my invention is: 
     
       1. A device for mixing a bone cement liquid with a bone cement powder to form liquid bone cement, the device comprising: a body having walls surrounding a closed body interior;   a vacuum port in a body wall;   a mixing chamber in the body;   a cement liquid chamber in a body wall;   a nozzle located in a body wall above the mixing chamber and in flow communication with the cement liquid chamber, said nozzle aimed at the mixing chamber and having a small flow passage; and   a cement stirring drive, the stirring drive including an operator on the outside of the body and a driven element on the inside of the body adjacent the mixing chamber.   
     
     
       2. The device as in claim 1 wherein said cement liquid chamber has an open upper end on the outside of the body, and including a lid for the cement liquid chamber, said lid moveable between a first position closing the cement liquid chamber and a second position away from the cement liquid chamber wherein cement liquid may be poured into such chamber when open. 
     
     
       3. The device as in claim 1 wherein the cement liquid chamber is located above the mixing chamber and the nozzle is aimed vertically down toward the mixing chamber. 
     
     
       4. The device as in claim 1 including a valve between the cement liquid chamber and the nozzle, the valve permitting flow of cement liquid from the cement liquid chamber to the nozzle when open and preventing flow to the nozzle when closed. 
     
     
       5. The device as in claim 4 wherein the valve includes a valve seat and a valve member having a rod extending into the cement liquid chamber and a head engageable with the valve seat. 
     
     
       6. The device as in claim 5 wherein an upper end of the valve member is located adjacent the upper end of the cement liquid chamber. 
     
     
       7. The device as in claim 6 including a lid for closing the cement liquid chamber, the lid having a surface engaging and depressing the upper end of the valve member when the lid closes the cement liquid chamber. 
     
     
       8. The device as in claim 1 wherein said operator comprises a rotary arm and said driven element comprises a rotary drive member having a drive surface, said member located above the mixing chamber. 
     
     
       9. The device as in claim 8 wherein said rotary drive member is located between the nozzle and the mixing chamber and includes an opening whereby a stream of liquid from the nozzle flows through the opening and into the mixing chamber. 
     
     
       10. The device as in claim 8 wherein said rotary drive member includes an alignment member facing the mixing chamber. 
     
     
       11. The device as in claim 1 wherein said nozzle has a flow passage with a cross sectional between about 0.0034 in 2  and about 0.00038 in 2 . 
     
     
       12. The device as in claim 1 including a valve between the cement liquid chamber and the nozzle, and a valve actuator on the outside of the housing. 
     
     
       13. The device as in claim 1 including a bone cement cartridge in said mixing chamber, a piston closing the bottom of the cartridge, a stirrer in the cartridge, a column of dry cement powder in the bottom of the cartridge, said nozzle located over said column of cement powder and to one side of the stirrer, a rotatable drive connection between the driven element and the stirrer, and a non-rotatable connection between the the body and the cartridge. 
     
     
       14. The device as in claim 13 wherein the driven element engages the body, the stirrer includes a lower end extending into the piston and the non-rotatable connection includes a connection between the piston and the housing. 
     
     
       15. The device as in claim 13 including an opening extending through the piston, the lower end of the stirrer extending into the opening, the stirrer having vertical surfaces and a uniform cross section to permit movement of the piston along the stirrer. 
     
     
       16. The device as in claim 1 including a cylindrical bone cement cartridge in said mixing chamber, a piston closing the bottom of the cartridge, a stirrer in the cartridge, a column of dry cement powder in the bottom of the cartridge, said nozzle located over said cartridge, a narrow high speed stream of bone cement liquid flowing through the nozzle, down into the cartridge and through the column of cement powder, said stream located away from the stirrer. 
     
     
       17. The device as in claim 16 including a cylinder of wetted cement powder surrounding the stream and extending along the height of the column. 
     
     
       18. The device as in claim 17 wherein said cylinder of wetted cement powder is spaced from the stream and including a cylindrical well between the stream and the cylinder of wetted cement powder. 
     
     
       19. The device as in claim 16 wherein the stream moves downwardly at a speed of between about 4.3 feet per second and about 10 feet per second, the pressure drop across the nozzle is about -12 PSI. 
     
     
       20. A device for mixing bone cement liquid with bone cement powder to form liquid bone cement, the device comprising: a body;   a mixing chamber in the body;   a cement liquid chamber in the body; and   a nozzle at the bottom of the liquid chamber, said nozzle aimed at the mixing chamber, said nozzle having a cross small cross sectional area for flowing a penetrating stream of bone cement liquid into the mixing chamber.   
     
     
       21. The device as in claim 20 including a pressure differential generator to flow cement liquid from the cement liquid chamber out the nozzle in said penetrating stream. 
     
     
       22. The device as in claim 20 wherein said cross sectional flow area is not substantially greater than 0.0034 in 2  and not substantially less than 0.00038 in 2 . 
     
     
       23. The device as in claim 20 including a valve between the liquid chamber and the nozzle. 
     
     
       24. The device as in claim 20 including a cement stirrer drive in the body, said drive including a driven element adjacent the mixing chamber, said element having a drive member adapted to engage a movable element in the mixing chamber. 
     
     
       25. The device as in claim 24 wherein the stirrer drive includes a rotary arm and said driven element comprises a rotary member located above the mixing chamber. 
     
     
       26. The device as in claim 25 wherein the rotary member is located between the nozzle and the mixing chamber and includes an opening permitting a stream of liquid from the nozzle to flow through the opening and into the mixing chamber. 
     
     
       27. The device as in claim 24 wherein said body includes walls defining a closed vacuum chamber, said mixing chamber and nozzle are located in the vacuum chamber, and including a vacuum port in the body. 
     
     
       28. The device as in claim 27 including cement liquid in the cement liquid chamber and nozzle, and a stream of cement liquid flowing from the nozzle down and into the mixing chamber at a speed of between about 4.3 feet per second and about 10 feet per second. 
     
     
       29. The device as in claim 28 wherein the pressure drop across the nozzle is about -12 PSI. 
     
     
       30. A method of mixing liquid bone cement from dry bone cement powder and bone cement liquid using a mixer of the type having a closed cement mixing chamber, comprising the steps of: (a) providing a column of dry bone cement powder in the mixing chamber, the column having a top and a bottom;   (b) evacuating the mixing chamber to remove air from the bone cement powder;   (c) providing a volume of bone cement liquid appropriate for mixing with the bone cement powder to form mixed liquid bone cement of a desired viscosity;   (d) flowing the volume of bone cement liquid down into the top of the column of bone cement powder in a narrow high speed stream having a fixed orientation without forming a puddle at the top of the column;   (e) moving the stream from the top of the column down to the bottom of the column, absorbing bone cement liquid from the stream into bone cement powder in the column to form a body of liquid-rich bone cement powder adjacent the stream extending from the top of the column to the bottom of the column while maintaining the bone cement powder in the column away from the body dry; and   (f) stirring the body of liquid-rich bone cement powder and the dry bone cement powder to form a liquid bone cement having the desired viscosity.   
     
     
       31. The method of claim 30 including the step of: (g) forming a body of liquid-rich bone cement powder surrounding the stream of bone cement liquid.   
     
     
       32. The method of claim 30 including the step of: (g) distributing the bone cement liquid in the body essentially uniformly along the height of the body from the top of the column to the bottom of the column.   
     
     
       33. The method of claim 30 including the step of: (g) flowing the stream of bone cement liquid vertically down into the column of bone cement powder.   
     
     
       34. The method of claim 30 including the step of: (g) forming a space between the stream and the body of liquid-rich bone cement powder.   
     
     
       35. The method of claim 34 including the steps of: (h) forming a cylindrical body of liquid-rich bone cement powder surrounding the stream; and   (i) forming a cylindrical space between the stream and the body of liquid-rich bone cement powder.   
     
     
       36. The method of claim 30 including the steps of: (g) generating the stream by flowing the bone cement liquid vertically down through a nozzle having a flow aperture while maintaining a pressure drop across the nozzle; and   (h) absorbing bone cement liquid from the stream into bone cement powder surrounding the stream.   
     
     
       37. The method of claim 36 including the step of: (i) absorbing bone cement liquid from the stream into a generally cylindrical body of liquid-rich bone cement powder surrounding the stream.   
     
     
       38. The method of claim 36 including the step of: (i) maintaining a pressure drop across the nozzle of about -12 PSI.   
     
     
       39. The method of claim 36 including the step of: (i) flowing the stream into the bone cement powder at a speed of between about 4.3 feet per second and about 10 feet per second.   
     
     
       40. The method of claim 36 including the step of: (i) flowing the bone cement liquid through a nozzle having a flow aperture with a cross sectional area between about 0.0034 in 2  and about 0.00038 in 2 .   
     
     
       41. The method of claim 36 including the step of: (i) maintaining a pressure drop across the nozzle of about -12 PSI and flowing the stream at a speed between about 4.3 feet per second and about 10 feet per second.   
     
     
       42. The method of claim 36 including the step of: (i) maintaining the size of the stream not appreciably greater than the size of the flow aperture in the nozzle.   
     
     
       43. The method of claim 36 including the step of: (i) forming a cylindrical space between the stream and the body of liquid-rich bone cement powder.   
     
     
       44. The method of claim 36 including the steps of: (i) placing the volume of bone cement liquid in a bone cement liquid chamber;   (j) closing the bone cement liquid chamber while leaving an air space over the bone cement liquid in the bone cement liquid chamber; and   (k) flowing the bone cement liquid from the closed bone cement liquid chamber to the nozzle to form the stream.   
     
     
       45. A method of mixing liquid bone cement from dry bone cement powder and bone cement liquid comprising the steps of: (a) providing a vertical column of dry bone cement powder in a mixing chamber;   (b) flowing a narrow high speed stream of bone cement liquid having a fixed orientation vertically down into and through the column of bone cement powder;   (c) absorbing bone cement liquid from the stream into dry bone cement powder in the column adjacent the stream to form a body of wetted bone cement powder extending from the top of the column to the bottom of the column;   (d) mixing the wetted bone cement powder with the dry bone cement powder in the chamber to form liquid bone cement having a substantially uniform viscosity.   
     
     
       46. The method of claim 45 including the step of: (e) flowing the bone cement liquid into the body without forming a liquid puddle on the top of the body.   
     
     
       47. The method of claim 46 including the step of: (f) absorbing bone cement liquid from the stream into dry bone cement powder in the column to form an annular body of wetted bone cement powder completely surrounding the stream.   
     
     
       48. The method of claim 47 including the step of: (g) forming a cylindrical body of wetted bone cement powder surrounding the stream.   
     
     
       49. The method of claim 48 including the step of: (h) forming a cylindrical passage between the stream and the cylinder of liquid-rich bone cement powder.   
     
     
       50. The method of claim 48 including the steps of: (h) removing air from the bone cement powder before flowing the stream of bone cement liquid into the powder.   
     
     
       51. The method of claim 48 including the step of: (h) forming said stream by flowing bone cement liquid through a nozzle having a cross sectional flow area of about 0.0034 in 2 .   
     
     
       52. The method of claim 51 including the step of: (i) maintaining a pressure drop across the nozzle of about -12 PSI.   
     
     
       53. The method of claim 45 including the steps of: (e) evacuating the mixing chamber;   (f) providing a cement liquid chamber above the mixing chamber;   (g) partially filling the cement liquid chamber with cement liquid leaving an air space at the top of the cement liquid chamber;   (h) closing the cement liquid chamber;   (i) flowing cement liquid from the closed cement liquid chamber through a nozzle and into the bone cement column to form the stream; and   (j) maintaining a pressure drop across the nozzle during flowing of cement liquid into the cement powder.   
     
     
       54. The method of claim 53 including the step of: (k) mixing the bone cement powder and liquid without substantial vertical movement of the powder and liquid.